The machine shop called me and told me my motor has to be bored a minimum of .20 over to get everything straight. I'm wanting to go .40 over to a 357-358 and i need a set of decent pistons.

Rob, if the block will clean up at 0.020" over, go w/that. There's no point to go w/a larger than needed oversize- there's no difference in power, and the smaller overbore will make for a more durable engine.

The 'best' piston for this case is a likely going to be a flat top, if you are starting w/a clean slate. You can use FT pistons and choose the cylinder head's chamber size to make the CR you need to go w/the camshaft that's going to be used, as well as what gas you plan to use.

But this can change if the heads you are going to use don't have the 'ideal' chamber size. Then, dished or domed pistons may be called for.